fix: use singular value, not a list for field filter expressions

Author: jwilkinson87

src/main/kotlin/com/ctrlhub/core/router/request/FilterExpression.kt

@@ -4,11 +4,8 @@ sealed interface FilterOption {
     fun format(): String
 }
 
-class FieldFilterExpression(val field: String, val values: List<String>) : FilterOption {
-    override fun format(): String {
-        val quoted = values.joinToString(",") { "'${it}'" }
-        return "${field}($quoted)"
-    }
+class FieldFilterExpression(val field: String, val value: String) : FilterOption {
+    override fun format(): String = "${field}('$value')"
 }
 
 class ValueFilterExpression(val value: String) : FilterOption {

src/test/kotlin/com/ctrlhub/core/router/request/RequestParametersFiltersTest.kt

@@ -9,8 +9,8 @@ class RequestParametersFiltersTest {
     fun `and of two field expressions formats correctly`() {
         val expr = AndExpression(
             listOf(
-                FieldFilterExpression("status", listOf("open")),
-                FieldFilterExpression("category", listOf("news"))
+                FieldFilterExpression("status", "open"),
+                FieldFilterExpression("category", "news")
             )
         )
 
@@ -39,7 +39,7 @@ class RequestParametersFiltersTest {
     fun `mixed and expression with field and function`() {
         val expr = AndExpression(
             listOf(
-                FieldFilterExpression("status", listOf("active")),
+                FieldFilterExpression("status", "active"),
                 ValueFilterExpression("is_latest()")
             )
         )